8/13/2019 ECEG-5401_2

1/37

Brushless DC (BLDC) motors are referred to as Brushless Permanent Magnet.Permanent Magnet AC motors, Permanent Magnet Synchronous Motors, etc.

The confusion arises because a brushless DC motor does not directly operate

off a DC voltage source. However, the basic principle of operation is similar to

a DC motor.

Brushless DC (BLDC) motors

SIMPLIFIED BLDC MOTOR DIAGRAMS

8/13/2019 ECEG-5401_2

2/37

*

*Halls Sensors sense theposition of the coils

* The Decoder Circuit turnsappropriate switches on andoff

* The voltage through thespecific coils turns the motor

8/13/2019 ECEG-5401_2

3/37

A Brushless DC Motor has:

A rotor with permanent magnets and a stator with windings

A BLDC motor is essentially a DC motor turned inside out

Brushes and commutator have been eliminated and the

windings are connected to the control electronics Control electronics replace the function of the commutator

and energize the proper winding

Windings are energized in a pattern which rotates around the

stator

The energized stator winding leads the rotor magnet, and

switches just as the rotor aligns with the stator

8/13/2019 ECEG-5401_2

4/37

There are no sparks

Potentially cleaner, faster, more efficient, less noisy and morereliable

Heat is generated in the stator: easier to remove and maintain

Rotor has permanent magnets vs. coils thus lighter less inertia:easier to start/stop

Linear torque/current relationship smooth accelerationor constant torque

Higher torque ripple due to lack of information between sectors

Low cost to manufacture

Simple, low-cost design for fixed-speed applications Clean, fast and efficient

Speed proportionate to line frequency (50 or 60 Hz)

Complex control for variable speed and torque

Require electronic control

Key Characteristics of the BLDC Motor

8/13/2019 ECEG-5401_2

5/37

How Does it work? The Brushless DC Motordoes not operate directly off a DC voltage source.

The brushless DC motor has a rotor with permanent magnets, a statorwith windings and commutation that is performed electronically.

Typically three Hall sensors are used to detect the rotor position and

commutation is performed based on Hall sensor inputs.

The motor is driven by rectangular or trapezoidal voltagestrokescoupled with the given rotor position.

The voltage strokes must be properly applied between the phases, so

that the angle between the stator flux and the rotor flux is kept close to

90 to get the maximum generated torque.

The position feedback is comprised using three Hall effect sensorsaligned with the back-EMF of the motor.

In sensorless control, back-EMF zero crossing is used for commutation.

8/13/2019 ECEG-5401_2

6/37

BLDC motor Drive Technique

Input:

Typically torque, speed, position and/or direction

Inputs can be analog voltage, potentiometer, switches or digital

communications

Feedback:

Hall effect sensors, optical encoder or back-EMF voltage

BLDC Motor Control:

Basic I/O for firmware bit-bang for 6-step #3 phase PWMs for hardwarePWM

Comparators for speed sensing in sensorless control, over-current

detection

Capture/Compare/PWM or input captures for speed sensing

8/13/2019 ECEG-5401_2

7/37

8/13/2019 ECEG-5401_2

8/37

Challenges of BLDC motor drive

Starting methods

Following the commutation sequence

Sensing the back-EMF(During sensorless application)

Back-EMF sensing techniques

The things we should have

Fast switching semiconductor devices

Very fast microprocessors Very organized algorithm

Free codes and algorithms are available in ti.comand microchip.com

8/13/2019 ECEG-5401_2

9/37

Contents

DC Motor (Brushed DC motor)

Brushless DC-Motor(BLDC)

Stepper Motor AC Induction Motor (ACIM)

Permanent Magnet Synchronous Motor (PMSM)

Switched Reluctance (SR) Motor

8/13/2019 ECEG-5401_2

10/37

Stepper Motor / Electro magnet

8/13/2019 ECEG-5401_2

11/37

Rotor

Stator

Coils

2

1

S

N

1

Outside Casing

Stator

Rotor

Internal components of a Stepper Motor

8/13/2019 ECEG-5401_2

12/37

2 2

1

N

S

1

S

N

Stators

Rotor

Cross Section of a Stepper Motor

8/13/2019 ECEG-5401_2

13/37

Four Steps per revolution i.e. 90 deg. steps.

Full Step Operation

8/13/2019 ECEG-5401_2

14/37

Eight steps per. revolution i.e. 45 deg. steps.

Half Step Operation

8/13/2019 ECEG-5401_2

15/37

2 2

1

1

S

N

S

N

NN

S S

1

a b

Winding number 1

2

b

Winding number 2

One

step6 pole rotor

8/13/2019 ECEG-5401_2

16/37

How many steps are required for one complete revolution?

Six pole rotor, two electro magnets.

8/13/2019 ECEG-5401_2

17/37

The top electromagnet (1) is turned on,attracting the nearest teeth of a gear-shaped iron rotor. With the teeth alignedto electromagnet 1, they will be slightlyoffset from electromagnet 2

The top electromagnet (1) is turnedoff, and the right electromagnet (2) isenergized, pulling the nearest teethslightly to the right. This results in arotation of 3.6 in this example.

Practical Stepper motor operation

8/13/2019 ECEG-5401_2

18/37

The bottom electromagnet (3) isenergized; another 3.6 rotationoccurs.

The left electromagnet (4) is enabled,rotating again by 3.6. When the topelectromagnet (1) is again enabled, theteeth in the sprocket will have rotated byone tooth position; since there are 25 teeth,it will take 100 steps to make a full rotationin this example.

8/13/2019 ECEG-5401_2

19/37

Stepping Motor to move read-write head

Stepper motor applications

8/13/2019 ECEG-5401_2

20/37

Paper feeder on printers

CNC lathes

Stepper motors

Stepper motor applications

8/13/2019 ECEG-5401_2

21/37

Rotor

Stator coils

CNC Stepping Motor

8/13/2019 ECEG-5401_2

22/37

Advantages:-

Low cost for control achieved

Ruggedness

Simplicity of construction

Can operate in an open loop control system

Low maintenance

Less likely to stall or slip

Will work in any environment

Disadvantages:-

Require a dedicated control circuit

Use more current than D.C. motors

High torque output achieved at low speeds

Advantages / Disadvantages

8/13/2019 ECEG-5401_2

23/37

Step 1 0 0 1 1

Step 2 1 0 1 0

Step 3 1 1 0 0

Step 4 0 1 0 1

+

CW CCW

Control sequence to turn a stepper motor

8/13/2019 ECEG-5401_2

24/37

The rotor of a permanent magnet stepper motorconsists of permanent magnetsand the stator which has two pairs of windings. Just as the rotor aligns with one of

the stator poles, the second phase is energized. The two phases alternate on and

off and also reverse polarity.

stepper motor drive

8/13/2019 ECEG-5401_2

25/37

There are four steps:

One phase lags the other phase by one step. This is equivalent to one-forth

of an electrical cycle or 90 Poles are formedusing a single magnet mounted in-line with the rotor axisand two pole pieces with many teeth

The teeth are staggeredto produce many poles The stator poles of a real stepper motor also have many teeth. The teeth

are arranged so that the two phases are still 90 out of phase

Key Characteristics of the Stepper Motor

Easy to position

moves in steps based on pulses suppliedto the stator windings

Direction of rotation is changed by reversing the pulse sequence

Speed is controlled by the frequency of pulses or pulse rate

8/13/2019 ECEG-5401_2

26/37

Stepper Control

Input: Inputs are typically pulses digital communications speed

Feedback:

Limits switches for homing and safety

Control:

Basic I/O for full-step and half-step control Comparators for over-current detection

Capture/Compare/PWM for micro stepping (or half stepping)

8/13/2019 ECEG-5401_2

27/37

Driver:

Multiple Switches (MOSFETS)

ULN2075B

8/13/2019 ECEG-5401_2

28/37

Micro Stepping Details

Each stepper motor will have a defined step angle associated with it.

Increases step resolution Divides a full step into sub-steps

Smoother transitions between

steps

Limits noise Reduces anti-

resonance problems

Maximum torque Low step rates High step rates

8/13/2019 ECEG-5401_2

29/37

8/13/2019 ECEG-5401_2

30/37

Applications

Idle speed adjust

Exhaust gas re-circulation Duct airflow vanes

Mirror control

Telescopes

Antennas

8/13/2019 ECEG-5401_2

31/37

Contents

DC Motor (Brushed DC motor)

Brushless DC-Motor(BLDC)

Stepper Motor

AC Induction Motor (ACIM)

8/13/2019 ECEG-5401_2

32/37

AC Induction Motor (ACIM)

The ACIM is comprised of a simple cage-like rotor and a stator

containing three windings

The changing field produced by the AC line current in the stator

induces a current in the rotor which interacts with the field and

causes the rotor to rotate

The rotor does not have any moving contacts, which eliminates

sparking

8/13/2019 ECEG-5401_2

33/37

Key Characteristics of the AC Induction Motor

Low cost to manufacture and maintain

Simple, low-cost design for fixed-speed applications Lower efficiency than other motor types

Speed proportionate to line frequency (50 or 60 Hz)

Complex control for variable speed and torque

Input:

Speed, frequency, torque, position, direction

Feedback:

Quadrature encoder, phase current

8/13/2019 ECEG-5401_2

34/37

Control:

Smooth control at low speeds

Efficient control at high speeds Complex control for variable speed and torque

Must know rotor position (velocity) for slip and vector control

Rotor position sensor is eliminated for sensorless vector control

strategies

Sensorless control does not work at low motor speeds

Driver: H-bridge for single phase

3-phase inverter for 3-phase motors

8/13/2019 ECEG-5401_2

35/37

Induction motor drive techniques

1. Vector controlVector control, also called field-oriented control(FOC), is a variablefrequency drive(VFD) control method which controls three-phaseAC

electric motoroutput by means of three controllable VFD inverter

output variables:

I. Voltage magnitudeII. Voltage angle

III. Freque control method which controls three-phaseAC

electric motoroutput by means.

2. V/Hz control

This type of controller is easy to apply in microcontroller based control

systems. And is useful in drive systems where torque is required to be constant.

Refer the attached slide.

http://en.wikipedia.org/wiki/Variable_frequency_drivehttp://en.wikipedia.org/wiki/Variable_frequency_drivehttp://en.wikipedia.org/wiki/Three-phasehttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Three-phasehttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Three-phasehttp://en.wikipedia.org/wiki/Three-phasehttp://en.wikipedia.org/wiki/Three-phasehttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Three-phasehttp://en.wikipedia.org/wiki/Three-phasehttp://en.wikipedia.org/wiki/Three-phasehttp://en.wikipedia.org/wiki/Variable_frequency_drivehttp://en.wikipedia.org/wiki/Variable_frequency_drive

8/13/2019 ECEG-5401_2

36/37

8/13/2019 ECEG-5401_2

37/37

END OF: INTRODUCTION TO POWER ELECTRONICS

AND ELECTRIC DRIVE

THANK YOU!